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| United States Patent |
6,258,522
|
|
Mariotti
, et al.
|
July 10, 2001
|
Silver bromoiodide core-shell grain emulsion
Abstract
The present invention relates to a light-sensitive emulsion, and a
light-sensitive photographic material containing the same, comprising
silver bromoiodide grains of a core shell structure comprising a) an inner
core consisting essentially of silver bromide or silver bromoiodide, the
silver iodide content of said inner core being within the range of 0 to 10
mole %, and b) a plurality of shells consisting essentially of silver
bromide or silver bromoiodide, wherein a pure silver iodide phase
representing from 0.1 to 5 mole % of the total silver halide grain content
is interposed between two adjacent shells, and wherein at least one of
said adjacent shells has a silver iodide content higher than 5 mole %.
| Inventors:
|
Mariotti; Mario (Carcare, IT);
Ghirardo; Stefania (Savona, IT);
Rocca; Giuseppe (Carcare, IT);
Avidano; Mauro (Asti, IT);
Gunnella; Alessandro (Savona, IT);
Astengo; Ezio (Bragno/Cairo Montenotte, IT)
|
| Assignee:
|
Ferrania S.p.A. (Savona, IT)
|
| Appl. No.:
|
576530 |
| Filed:
|
May 23, 2000 |
Foreign Application Priority Data
| Current U.S. Class: |
430/567; 430/569 |
| Intern'l Class: |
G03C 001/005 |
| Field of Search: |
430/567,569
|
References Cited
U.S. Patent Documents
| 4477564 | Oct., 1984 | Cellone et al. | 430/567.
|
| 4614711 | Sep., 1986 | Sugimoto et al. | 430/567.
|
| 4668614 | May., 1987 | Takada et al. | 430/567.
|
| 4728602 | Mar., 1988 | Shibahara et al. | 430/567.
|
| 5780216 | Jul., 1998 | Ihama | 430/567.
|
| 5906914 | May., 1999 | Taguchi et al. | 430/567.
|
| 5955253 | Sep., 1999 | Kawakami | 430/568.
|
| 5965344 | Oct., 1999 | Ando et al. | 430/567.
|
| 6007977 | Dec., 1999 | Nishikawa | 430/567.
|
| Foreign Patent Documents |
| 202 784 | Apr., 1986 | EP.
| |
| 0202784 | Sep., 1991 | EP.
| |
| 0299719 | Jan., 1993 | EP.
| |
Primary Examiner: Baxter; Janet
Assistant Examiner: Walke; Amanda C.
Attorney, Agent or Firm: Mark A. Litman & Assoc., Litman; Mark A.
Claims
What is claimed is:
1. A light-sensitive emulsion comprising silver bromoiodide grains of a
core shell structure comprising:
a) an inner core consisting essentially of silver bromide or silver
bromoiodide, the silver iodide content of said inner core being within the
range of 0 to 20 mole %, and
b) an odd plurality of three or five shells consisting essentially of
silver bromide or silver bromoiodide,
wherein a pure silver iodide phase representing from 0.1 to 5 mole % of the
total silver halide grain content is interposed between two adjacent
shells, and wherein at least one of said adjacent shells has a silver
iodide content higher than 10 mole %.
2. The light-sensitive emulsion according to claim 1, wherein said inner
core consists essentially of silver bromide.
3. The light-sensitive emulsion according to claim 1, wherein said silver
bromoiodide grains have an average iodide content ranging from 1 to 10 mol
%, relative to the total halide content of the grains.
4. The light-sensitive emulsion according to claim 1, wherein the silver
content of said inner core ranges from 20 to 70 mol % relative to the
total silver content of the grain and the silver content of each shell of
said plurality of shells ranges from 5 to 40 mol % relative to the total
silver content of the grain.
5. The light-sensitive emulsion according to claim 1, wherein said
plurality of shells comprises at least:
a) an inner shell consisting essentially of silver bromide or silver
bromoiodide, the silver iodide content of said inner shell being within
the range of from 0 to 40 mole %,
b) a pure silver iodide phase on the inner shell representing from 0.1 to 5
mole % of the total silver halide grain content, and
b) an outer shell on the pure silver iodide phase consisting essentially of
silver bromide or silver bromoiodide, the silver iodide content of said
outer shell being within the range of from 0 to 40 mole % wherein at least
one of said inner or outer shells has a silver iodide content higher than
5 mole %.
6. The light-sensitive emulsion according to claim 5, wherein said
plurality of shells further comprises a first innermost shell on the core,
said innermost shell consisting essentially of silver bromoiodide with a
silver iodide content within the range of from 2 to 20 mole % and an
outermost shell consisting essentially of silver bromide.
7. A light-sensitive silver halide photographic material comprising a
support and at least on silver halide emulsion layer which comprises
silver bromoiodide grains of a core shell structure comprising:
a) an inner core consisting essentially of silver bromide or silver
bromoiodide, the silver iodide content of said inner core being within the
range of 0 to 20 mole %, and
b) an odd plurality of three or five shells consisting essentially of
silver bromide or silver bromoiodide,
wherein a pure silver iodide phase representing from 0.1 to 5 mole % of the
total silver halide grain content is interposed between two adjacent
shells, and wherein at least one of said adjacent shells has a silver
iodide content higher than 10 mole %.
8. The light-sensitive silver halide photographic material according to
claim 7, wherein said inner core consists essentially of silver bromide.
9. The light-sensitive silver halide photographic material according to
claim 7, wherein said silver bromoiodide grains have an average iodide
content ranging from 1 to 15 mol %, relative to the total halide content
of the grains.
10. The light-sensitive silver halide photographic material according to
claim 7, wherein the silver content of said inner core ranges from 20 to
70 mol % relative to the total silver content of the grain and the silver
content of each shell of said plurality of shells ranges from 5 to 40 mol
% relative to the total silver content of the grain.
11. A light-sensitive emulsion comprising silver bromoiodide grains of a
core shell structure comprising:
a) an inner core consisting essentially of silver bromide or silver
bromoiodide, the silver iodide content of said inner core being within the
range of 0 to 20 mole %, and
b) a plurality of an odd number of shells consisting essentially of silver
bromide or silver bromoiodide,
wherein a pure silver iodide phase representing from 0.1 to 5 mole % of the
total silver halide grain content is interposed between two adjacent
shells, and wherein at least one of said adjacent shells has a silver
iodide content higher than 10 mole %.
12. A light-sensitive silver halide photographic material comprising a
support and at least on silver halide emulsion layer which comprises
silver bromoiodide grains of a core shell structure comprising:
a) an inner core consisting essentially of silver bromide or silver
bromoiodide, the silver iodide content of said inner core being within the
range of 0 to 20 mole %, and
b) a plurality of an odd number of shells consisting essentially of silver
bromide or silver bromoiodide,
wherein a pure silver iodide phase representing from 0.1 to 5 mole % of the
total silver halide grain content is interposed between two adjacent
shells, and wherein at least one of said adjacent shells has a silver
iodide content higher than 10 mole %.
Description
FIELD OF THE INVENTION
The present invention relates to photographic silver halide core-shell
emulsions. More particularly, the invention relates to a silver
bromoiodide emulsion having grains comprising several phases with
different iodide content, which emulsion shows better granularity and
sensitometric properties.
BACKGROUND OF THE ART
There have been more strict requirements for silver halide emulsions for
photographic use, which has increased the demands for the high level
photographic characteristics such as, for example, high speed, excellent
graininess, high sharpness, low fog, wider exposure latitude range and so
on.
The above mentioned requirements have been satisfied by well-known silver
bromoiodide grain emulsions having a high silver iodide content in the
inner part of the grains and a specific core-shell structure in the grains
thereof. It is well known in the photographic art that light absorbing
increases in the order of silver chloride, silver bromide and silver
iodide, but development activity correspondingly decreases in the same
order. By using the above described core-shell silver bromoiodide
emulsions, a good balance between light sensitivity and development
activity has been obtained.
Examples of core-shell silver bromoiodide emulsion are described in many
patent and literature references. For example, U.S. Pat. No. 4,668,614 and
U.S. Pat. No. 4,728,602 describe a monodispersed core-shell silver
bromoiodide emulsion having a core part comprising a silver iodide content
of 10 to 45 mol % and a shell part comprising a silver iodide content
lower than 5 mol %., with an average silver iodide content higher than 7
mol %. When examined by X-ray diffractometry, two peaks are evidentiated.
The first one corresponding to the high iodide core part, the second one
to the low iodide shell part. According to the claimed invention it is
preferred to have a ratio between the diffraction intensity of the two
peaks in the range of from 1/10 to 3/1, more preferably 1/3 to 3/1.
Similarly, European application EP 299,719 discloses a core-shell silver
halide emulsion having a core comprising not less than 10 mol % of silver
iodide, at least one shell consisting of silver bromide or silver
bromoiodide, the outermost of which has a silver iodide content not higher
than 5 mol %, and an average silver iodide content of not less than 10 mol
%.
EP 309,119 discloses a core-shell silver halide emulsion having at least
three silver bromide or silver bromoiodide phases of different
composition. According to a preferred embodiment of the claimed emulsion,
the innermost phase has a silver iodide content of at least 10 mol %, the
outermost phase has a silver iodide content of not more than 6 mol %, and
the intermediate phase has a silver iodide content difference with the
outermost or innermost phase of at least 3 mol %. When examined by X-ray
diffraction, the claimed emulsion shows three or more diffraction peaks,
each corresponding to a phase containing a different percentage of iodide.
EP 202,784 describes a core-shell type silver halide emulsion having an
inner core essentially consisting of silver bromide or silver bromoiodide
and a plurality of shells. The outermost shell has a silver iodide content
ranging from 0 to 10 mol %, the innermost shell has a silver iodide
content at least 6 mol % higher than that of the outermost shell, and an
intermediate shell has a silver iodide content is at least 3 mol % lower
than that of the innermost shell and at least 3 mol % higher than that of
the outermost shell.
U.S. Pat. No. 4,477,564 describes a multiphase bromoiodide emulsion having
an average silver iodide content higher than 12%.
U.S. Pat. No. 4,614,711 describes silver bromoiodide grains with a core
shell structure with a core of silver bromide or bromiodide and a first
layer composed of silver bromoiodide, exterior to said core and containing
more iodide than said core by 10 mol % or more.
U.S. Pat. No. 5,780,216 discloses a color negative silver halide
photographic material with a core shell emulsion having a plurality of
shells comprising an inner core consisting essentialy of silver bromide or
bromoiodide and a plurality of shells of silver bromide or silver
bromoiodide comprising a high iodide shell interposed between two shells
consisting essentially of silver bromide.
SUMMARY OF THE INVENTION
The present invention relates to a light-sensitive emulsion comprising
silver bromoiodide grains of a core shell structure comprising:
a) an inner core consisting essentially of silver bromide or silver
bromoiodide, the silver iodide content of said inner core being within the
range of 0 to 10 mole %, and
b) a plurality of shells consisting essentially of silver bromide or silver
bromoiodide,
wherein a pure silver iodide phase representing from 0.1 to 5 mole % of the
total silver halide grain content is interposed between two adjacent
shells, and wherein at least one of said adjacent shells has a silver
iodide content higher than 5 mole %.
DETAILED DESCRIPTION OF THE INVENTION
The light-sensitive emulsion of the present invention comprises silver
bromoiodide grains having an inner core and a plurality of shells. The
inner core consists essentially of silver bromide or silver bromoiodide.
The plurality of shells consists essentially of silver bromide or silver
bromoiodide having different compositions.
The silver iodide content of the inner core is in the range of from 0 to 20
mol % relative to the total silver halide content of the inner core phase,
preferably from 0 to 10 mol %, and more preferably from 0 to 5 mol %.
According to the most preferred aspect of the present invention the inner
core consists essentially of silver bromide.
The silver iodide content of each shell is in the range of from 0 to 40 mol
%, preferably from 0 to 20 mol % relative to the total silver halide
content of the shell. The plurality of shells comprises at least two
shells having different silver halide composition.
The minimal core-shell structure of the silver halide grains according to
the present invention consists in an inner core and two shells surrounding
the inner core. The number of shells surrounding the inner core preferably
ranges from two to four. Accordingly, the core-shell structure of the
silver halide grains according to the present invention consists in an
inner core, an innermost shell adjacent the inner core, an outermost
shell, and, optionally, one or more intermediate shells interposed between
the innermost shell and the outermost shell. Preferably, the innermost
shell adjacent to the inner core has a silver bromoiodide composition,
with a silver iodide content of from 2 to 20 mol %, most preferably from 3
to 10 mol % relative to the total silver halide content of the shell, and
the outermost shell has a silver bromide composition. The intermediate
shells can have a silver bromide or silver bromoiodide composition, with a
silver iodide content ranging from 0 to 40 mol %, preferably from 0 to 20
mol % relative to the total silver halide content of the shell.
The silver content of the core and the plurality of shells relative to the
total silver content of the grain can have different values depending on
the number of shells representing the plurality of shells. Preferably, the
silver content of the inner core represents from 20 to 70 mol %, more
preferably from 30 to 60 mol % relative to the total silver content of the
grain. Preferably, the silver content of the plurality of shells
represents from 30 to 80 mol %, more preferably from 40 to 70 mol %
relative to the total silver content of the grain. Each shell can have a
silver content ranging from 5 to 40 mol %, preferably from 10 to 25 mol %
relative to the total silver content of the grain.
According to the essential aspect of the present invention, a pure silver
iodide phase is interposed between two adjacent shells The pure silver
iodide phase has a silver content of from 0.1 to 5 mol %, preferably from
1 to 3 mol % relative to the total silver content of the grain.
According to the second essential aspect of the present invention, at least
one of the two adjacent shells surrounding the above mentioned pure silver
iodide phase (that is, the two shells in contact with the pure silver
iodide phase) has a silver iodide content higher than 5 mole %, preferably
higher than 10 mole % relative to the total silver halide content of the
shell.
The average iodide content of the silver halide emulsion grains according
to the invention ranges from 1 to 15 mol %, preferably from 2 to 10 mol %,
and more preferably from 3 to 6 mol % relative to the total halide content
of the emulsion grains.
Accordingly, the core shell emulsion according to the present invention can
be represented by the following, not limitative examples:
Core: AgBr
Shell: AgBr.sub.85% I.sub.15%
Pure iodide phase
Shell: AgBr
Core: AgBr
Shell: AgBr.sub.95% I.sub.5%
Shell: AgBr.sub.85% I.sub.15%
Pure iodide phase
Shell: AgBr.sub.95% I.sub.5%
Shell: AgBr
Core: AgBr
Shell: AgBr.sub.95% I.sub.5%
Shell: AgBr
Pure iodide phase
Shell: AgBr.sub.85% I.sub.10%
Core: AgBr
Shell: AgBr.sub.95% I.sub.4%
Pure iodide phase
Shell: AgBr.sub.85% I.sub.15%
Core: AgBr
Shell: AgBr.sub.95% I.sub.5%
Shell: AgBr.sub.80% I.sub.20%
Pure iodide phase
Shell: AgBr
Core: AgBr
Shell: AgBr.sub.95% I.sub.5%
Shell: AgBr
Pure iodide phase
Shell: AgBr.sub.85% I.sub.15%
Shell: AgBr
According to a more preferred aspect of the present invention the core
shell grains have a structure comprising a silver bromide inner core, an
innermost shell shell consisting essentially of silver bromoiodide with a
silver iodide content of from more than 2 to 20 mole %, preferably from 3
to 17 mole %, a pure silver iodide phase representing from 0.1 to 5 mole %
of the total silver halide grain content, and an outermost shell
consisting essentially of silver bromide.
According to the most preferred aspect of the present invention the core
shell grains have a structure comprising a silver bromide inner core, an
innermost shell consisting essentially of silver bromoiodide with a silver
iodide content within the range of from 2 to 20 mole %, an intermediate
shell consisting essentially of silver bromide, a pure silver iodide phase
representing from 0.1 to 5 mole % of the total silver halide grain
content, another intermediate shell consisting essentially of silver
bromoiodide with a silver iodide content of from more than 5 mole % to 20
mole %, and an outermost shell consisting essentially of silver bromide.
The wording "consisting essentially of silver bromide or silver bromoioide"
widely employed hereinabove in describing the core-shell emulsion
according to the present invention means that the amount of halides
different than iodide and bromide is less than 3 mole %.
The light-sensitive emulsion of the present invention is preferably
monodispersed, and the coefficient of variation of the distribution (COV)
is preferably lower than 0.30, more preferably lower than 0.20, and most
preferably lower than 0.15. The COV is a value obtained by dividing the
distribution (standard deviation) of the grain size in terms diameter of a
projected area of each grain, by the average grain size.
The silver iodobromide grains of the emulsion of the present invention may
be regular grains having a regular crystal structure such as cube,
octahedron, and tetradecahedron, or the spherical or irregular crystal
structure, or those having crystal defects such as twin plane, or those
having a tabular form, or the combination thereof.
The term "cubic grains" according to the present invention is intended to
include substantially cubic grains, that is silver iodobromide grains
which are regular cubic grains bounded by crystallographic faces (100), or
which may have rounded edges and/or vertices or small faces (111), or may
even be nearly spherical when prepared in the presence of soluble iodides
or strong ripening agents, such as ammonia. Particularly good results are
obtained with silver bromoiodide grains having average grain sizes in the
range from 0.2 to 3 .mu.m, more preferably from 0.4 to 1.5 .mu.m.
Preparation of silver halide emulsions comprising cubic silver iodobromide
grains is described, for example, in Research Disclosure, Vol. 184, Item
18431, Vol.176, Item 17644 and Vol. 308, Item 308119.
Other iodobromide emulsions according to this invention are those which
employ one or more light-sensitive tabular grain emulsions. The tabular
silver bromoiodide grains contained in the emulsion of this invention have
an average diameter:thickness ratio (often referred to in the art as
aspect ratio) of at least 2:1, preferably 2:1 to 20:1, more preferably 3:1
to 14:1, and most preferably 3:1 to 8:1. Average diameters of the tabular
silver bromoiodide grains suitable for use in this invention range from
about 0.3 .mu.m to about 5 .mu.m, preferably 0.5 .mu.m to 3 .mu.m, more
preferably 0.8 .mu.m to 1.5 .mu.m. The tabular silver bromoiodide grains
suitable for use in this invention have a thickness of less than 0.4
.mu.m, preferably less than 0.3 .mu.m and more preferably less than 0.2
.mu.m.
The tabular grain characteristics described above can be readily
ascertained by procedures well known to those skilled in the art. The term
"diameter" is defined as the diameter of a circle having an area equal to
the projected area of the grain. The term "thickness" means the distance
between two substantially parallel main planes constituting the tabular
silver halide grains. From the measure of diameter and thickness of each
grain the diameter:thickness ratio of each grain can be calculated, and
the diameter:thickness ratios of all tabular grains can be averaged to
obtain their average diameter:thickness ratio. By this definition the
average diameter:thickness ratio is the average of individual tabular
grain diameter:thickness ratios. In practice, it is simpler to obtain an
average diameter and an average thickness of the tabular grains and to
calculate the average diameter:thickness ratio as the ratio of these two
averages. Whatever the used method may be, the average diameter:thickness
ratios obtained do not greatly differ.
In the silver halide emulsion layer containing tabular silver halide
grains, at least 15%, preferably at least 25%, and, more preferably, at
least 50% of the silver halide grains are tabular grains having an average
diameter:thickness ratio of not less than 2:1. Each of the above
proportions, "15%", "25%" and "50%" means the proportion of the total
projected area of the tabular grains having a diameter: thickness ratio of
at least 2:1 and a thickness lower than 0.4 .mu.m, as compared to the
projected area of all of the silver halide grains in the layer.
It is known that photosensitive silver halide emulsions can be formed by
precipitating silver halide grains in an aqueous dispersing medium
comprising a binder, gelatin preferably being used as a binder.
The silver halide grains may be precipitated by a variety of conventional
techniques. The silver halide emulsion can be prepared using a single-jet
method, a double-jet method, or a combination of these methods or can be
matured using, for instance, an ammonia method, a neutralization method,
an acid method, or can be performed an accelerated or constant flow rate
precipitation, interrupted precipitation, ultrafiltration during
precipitation, etc. References can be found in Trivelli and Smith, The
Photographic Journal, Vol. LXXIX, May 1939, pp. 330-338, T. H. James, The
Theory of The Photographic Process, 4th Edition, Chapter 3, U.S. Pat. Nos.
2,222,264, 3,650,757, 3,917,485, 3,790,387, 3,716,276, 3,979,213, Research
Disclosure, December 1989, Item 308119 "Photographic Silver Halide
Emulsions, Preparations, Addenda, Processing and Systems", and Research
Disclosure, September 1976, Item 14987.
One common technique is a batch process commonly referred to as the
double-jet precipitation process by which a silver salt solution in water
and a halide salt solution in water are concurrently added into a reaction
vessel containing the dispersing medium.
In the double jet method, in which alkaline halide solution and silver
nitrate solution are concurrently added in the gelatin solution, the shape
and size of the formed silver halide grains can be controlled by the kind
and concentration of the solvent existing in the gelatin solution and by
the addition speed. Double-jet precipitation processes are described, for
example, in GB 1,027,146, GB 1,302,405, U.S. Pat. No. 3,801,326, U.S. Pat.
No. 4,046,376, U.S. Pat. No. 3,790,386, U.S. Pat. No. 3,897,935, U.S. Pat.
No. 4,147,551, and U.S. Pat. No. 4,171,224.
The single jet method in which a silver nitrate solution is added in a
halide and gelatin solution has been long used for manufacturing
photographic emulsion. In this method, because the varying concentration
of halides in the solution determines which silver halide grains are
formed, the formed silver halide grains are a mixture of different kinds
of shapes and sizes.
Precipitation of silver halide grains usually occurs in two distinct
stages. In a first stage, nucleation, formation of fine silver halide
grain occurs. This is followed by a second stage, the growth stage, in
which additional silver halide formed as a reaction product precipitates
onto the initially formed silver halide grains, resulting in a growth of
these silver halide grains. Batch double-jet precipitation processes are
typically undertaken under conditions of rapid stirring of reactants in
which the volume within the reaction vessel continuously increases during
silver halide precipitation and soluble salts are formed in addition to
the silver halide grains.
In order to avoid soluble salts in the emulsion layers of a photographic
material from crystallizing out after coating and other photographic or
mechanical disadvantages (stickiness, brittleness, etc.), the soluble
salts formed during precipitation have to be removed.
In preparing the silver halide emulsions of the present invention, a wide
variety of hydrophilic dispersing agents for the silver halides can be
employed. As hydrophilic dispersing agent, any hydrophilic polymer
conventionally used in photography can be advantageously employed
including gelatin, a gelatin derivative such as acylated gelatin, graft
gelatin, etc., albumin, gum arabic, agar agar, a cellulose derivative,
such as hydroxyethylcellulose, carboxymethylcellulose, etc., a synthetic
resin, such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide,
etc. Other hydrophilic materials useful known in the art are described,
for example, in Research Disclosure, Vol. 308, Item 308119, Section IX.
The core-shell silver bromoiodide emulsion of the present invention can be
prepared according to the following processing method. For sake of
clarity, the following description was limited to the preparation of a
core-shell emulsion comprising two shells, but the present invention is
not intended to be limited to such a constructions.
1. An aqueous solution prepared by dissolving gelatin, a bromide salt, and,
optionally a iodide salt in distilled water was provided in a reaction
vessel. The solution was stirred by a dispersator and kept at about
30.degree. to 60.degree. C.
2. To the resulting solution, an aqueous silver salt solution and an
aqueous bromide salt solution were added by double jet under stirring, by
keeping constant the temperature at about 30.degree. to 60.degree. C. The
double jet addition of silver and bromide salts can be repeated one or
more times, by varying the addition conditions (pAg, rate of addition,
etc.) until to reach the precipitation of the total silver requested for
the formation of the core. The rate of addition kept constant in the range
of from 5 to 60 ml/minute or can vary from an initial flow of from 5 to 30
ml/minute, to a final flow of from 20 to 60 ml/minute. The accelerated
double jet profile can be linear, quadratic, or step-by-step, by employing
silver and bromide salt solutions with different concentrations.
Optionally, an iodide salt aqueous solution can be added during the
growth.
4. To the resulting dispersion, an aqueous silver salt solution, an aqueous
bromide salt solution, and, optionally, an aqueous iodide salt solution
were added under stirring. The bromide and iodide salts can also be added
from a single solution. The rate of addition can be kept constant in the
range of from 5 to 60 ml/minute or can vary from an initial flow of from 5
to 30 ml/minute, to a final flow of from 20 to 60 ml/minute. The
accelerated double jet profile can be linear, quadratic, or step-by-step,
by employing silver and bromide salt solutions with different
concentrations.
5. After the addition of an ammonia solution, an aqueous iodide salt
solution was added at constant rate in a period of from one to five
minutes.
6. After neutralizing the ammonia added during step 5, an aqueous silver
salt solution, an aqueous bromide salt solution, and, optionally, an
aqueous iodide salt solution were added under stirring. The bromide and
iodide salts can also be added from a single solution. The rate of
addition can be kept constant in the range of from 5 to 60 ml/minute or
can vary from an initial flow of from 5 to 30 ml/minute, to a final flow
of from 20 to 60 ml/minute. The accelerated double jet profile can be
linear, quadratic, or step-by-step, by employing silver and bromide salt
solutions with different concentrations.
The silver halide grain emulsion of the present invention can be chemically
sensitized using sensitizing agents known in the art. Sulfur containing
compounds, gold and noble metal compounds, and polyoxylakylene compounds
are particularly suitable. In particular, the silver halide emulsions may
be chemically sensitized with a sulfur sensitizer, such as sodium
thiosulfate, allylthiocyanate, allylthiourea, thiosulfinic acid and its
sodium salt, sulfonic acid and its sodium salt, allylthiocarbamide,
thiourea, cystine, etc.; an active or inert selenium sensitizer; a
reducing sensitizer such as stannous salt, a polyamine, etc.; a noble
metal sensitizer, such as gold sensitizer, more specifically potassium
aurithiocyanate, potassium chloroaurate, etc.; or a sensitizer of a water
soluble salt such as for instance of ruthenium, rhodium, iridium and the
like, more specifically, ammonium chloropalladate, potassium
chloroplatinate and sodium chloropalladite, etc.; each being employed
either alone or in a suitable combination. Other useful examples of
chemical sensitizers are described, for example, in Research Disclosure
17643, Section III, 1978 and in Research Disclosure 308119, Section 111,
1989.
The silver halide emulsion of the present invention can be spectrally
sensitized with dyes from a variety of classes, including the polymethyne
dye class, which includes the cyanines, merocyanines, complex cyanines and
merocyanines, oxonols, hemioxonols, styryls, merostyryls, and
streptocyanine.
The cyanine spectral sensitizing dyes include, joined by a methine linkage,
two basic heterocyclic nuclei, such as those derived from quinoline,
pyrimidine, isoquinoline, indole, benzindole, oxazole, thiazole,
selenazole, imidazole, benzoxazole, benzothiazole, benzoselenazole,
benzoimidazole, naphthoxazole, naphthothiazole, naphthoselenazole,
tellurazole, oxatellurazole.
The merocyanine spectral sensitizing dyes include, joined by a methine
linkage, a basic heterocyclic nucleus of the cyanine-dye type and an
acidic nucleus, which can be derived from barbituric acid,
2-thiobarbituric acid, rhodanine, hydantoin, 2-thiohydantoin,
2-pirazolin-5-one, 2-isoxazolin-5-one, indan-1,3-dione,
cyclohexane-1,3-dione, 1,3-dioxane-4,6-dione, pyrazolin-3,5-dione,
pentane-2,4-dione, alkylsulfonylacetonitrile, malononitrile,
isoquinolin-4-one, chromane-2,4-dione, and the like.
One or more spectral sensitizing dyes may be used. Dyes with sensitizing
maxima at wavelengths throughout the visible and infrared spectrum and
with a great variety of spectral sensitivity curve shapes are known. The
choice and relative proportion of dyes depends on the region of the
spectrum to which sensitivity is desired and on the shape of the spectral
sensitivity desired.
Examples of sensitizing dyes can be found in Venkataraman, The chemistry of
Synthetic Dyes, Academic Press, New York, 1971, Chapter V, James, The
Theory of the Photographic Process, 4th Ed., Macmillan, 977, Chapter 8, F.
M. Hamer, Cyanine Dyes and Related Compounds, John Wiley and Sons, 1964.
The silver halide emulsion of the present invention can be used for the
manufacture of light-sensitive silver halide photographic elements, in
particular color negative photographic elements, color reversal
photographic elements, and the like.
Silver halide multilayer color photographic elements usually comprise,
coated on a support, a red sensitized silver halide emulsion layer
associated with cyan dye-forming color couplers, a green sensitized silver
halide emulsion layer associated with magenta dye-forming color couplers
and a blue sensitized silver halide emulsion layer associated with yellow
dye-forming color couplers. Each layer can be comprised of a single
emulsion layer or of multiple emulsion sub-layers sensitive to a given
region of visible spectrum. When multilayer materials contain multiple
blue, green or red sub-layers, there can be in any case relatively faster
and relatively slower sub-layers. These elements additionally comprise
other non-light sensitive layers, such as intermediate layers, filter
layers, antihalation layers and protective layers, thus forming a
multilayer structure. These color photographic elements, after imagewise
exposure to actinic radiation, are processed in a chromogenic developer to
yield a visible color image. The layer units can be coated in any
conventional order, but in a preferred layer arrangement the red-sensitive
layers are coated nearest the support and are overcoated by the
green-sensitive layers, a yellow filter layer and the blue-sensitive
layers.
Suitable color couplers are preferably selected from the couplers having
diffusion preventing groups, such as groups having a hydrophobic organic
residue of about 8 to 32 carbon atoms, introduced into the coupler
molecule in a non-splitting-off position. Such a residue is called a
"ballast group". The ballast group is bonded to the coupler nucleus
directly or through an imino, ether, carbon-amido, sulfonamido, ureido,
ester, imido, carbamoyl, sulfamoyl bond, etc. Examples of suitable
ballasting groups are described in U.S. Pat. No. 3,892,572.
Said non-diffusible couplers are introduced into the light-sensitive silver
halide emulsion layers or into non-light-sensitive layers adjacent
thereto. On exposure and color development, said couplers give a color
which is complementary to the light color to which the silver halide
emulsion layers are sensitive. Consequently, at least one non-diffusible
cyan-image forming color coupler, generally a phenol or an
.alpha.-naphthol compound, is associated with red-sensitive silver halide
emulsion layers, at least one non-diffusible magenta image-forming color
coupler, generally a 5-pyrazolone or a pyrazolotriazole compound, is
associated with green-sensitive silver halide emulsion layers and at least
one non-diffusible yellow image forming color coupler, generally a
acylacetanilide compound, is associated with blue-sensitive silver halide
emulsion layers.
Said color couplers may be 4-equivalent and/or 2-equivalent couplers, the
latter requiring a smaller amount of silver halide for color production.
As is well known, 2-equivalent couplers derive from 4-equivalent couplers
since, in the coupling position, they contain a substituent which is
released during coupling reaction. 2-Equivalent couplers which may be used
in silver halide color photographic elements include both those
substantially colorless and those which are colored ("masked couplers").
The 2-equivalent couplers also include white couplers which do not form
any dye on reaction with the color developer oxidation products. The
2-equivalent color couplers include also DIR couplers which are capable of
releasing a diffusing development inhibiting compound on reaction with the
color developer oxidation products.
The most useful cyan-forming couplers are conventional phenol compounds and
.alpha.-naphthol compounds. Examples of cyan couplers can be selected from
those described in U.S. Pat. Nos. 2,369,929; 2,474,293; 3,591,383;
2,895,826; 3,458,315; 3,311,476; 3,419,390; 3,476,563 and 3,253,924; and
in British patent 1,201,110.
The most useful magenta-forming couplers are conventional pyrazolone type
compounds, indazolone type compounds, cyanoacetyl compounds,
pyrazoletriazole type compounds, etc, and particularly preferred couplers
are pyrazolone type compounds. Magenta-forming couplers are described for
example in U.S. Pat. Nos. 2,600,788, 2,983,608, 3,062,653, 3,127,269,
3,311,476, 3,419,391, 3,519,429, 3,558,319, 3,582,322, 3,615,506,
3,834,908 and 3,891,445, in DE patent 1,810,464, in DE patent applications
2,408,665, 2,417,945, 2,418,959 and 2,424,467 and in JP patent
applications 20,826/76, 58,922/77, 129,538/74, 74,027/74, 159,336/75,
42,121/77, 74,028/74, 60,233/75, 26,541/76 and 55,122/78.
The most useful yellow-forming couplers are conventional open-chain
ketomethylene type couplers. Particular examples of such couplers are
benzoylacetanilide type and pivaloyl acetanilide type compounds.
Yellow-forming couplers that can be used are specifically described in
U.S. Pat. Nos. 2,875,057, 3,235,924, 3,265,506, 3,278,658, 3,369,859,
3,408,194, 3,415,652 3,528,322, 3,551,151, 3,682,322, 3,725,072 and
3,891,445, in DE patents 2,219,917, 2,261,361 and 2,414,006, in GB patent
1,425,020, in JP patent 10,783/76 and in JP patent applications 26,133/72,
73,147/73, 102,636/76, 6,341/75, 123,342/75, 130,442/75, 1,827/76,
87,650/75, 82,424/77 and 115,219/77.
Colored couplers can be used which include those described for example in
U.S. Pat. Nos. 3,476,560, 2,521,908 and 3,034,892, in JP patent
publications 2,016/69, 22,335/63, 11,304/67 and 32,461/69, in JP patent
applications 26,034/76 and 42,121/77 and in DE patent application
2,418,959. The light-sensitive silver halide color photographic element
may contain high molecular weight color couplers as described for example
in U.S. Pat. No. 4,080,211, in EP Pat. Appl. No. 27,284 and in DE Pat.
Appl. Nos. 1,297,417, 2,407,569, 3,148,125, 3,217,200, 3,320,079,
3,324,932, 3,331,743, and 3,340,376.
Colored cyan couplers can be selected from those described in U.S. Pat.
Nos. 3,934,802; 3,386,301 and 2,434,272, colored magenta couplers can be
selected from the colored magenta couplers described in U.S. Pat. Nos.
2,434,272; 3,476,564 and 3,476,560 and in British patent 1,464,361.
Colorless couplers can be selected from those described in British patents
861,138; 914,145 and 1,109,963 and in U.S. Pat. No. 3,580,722.
Also, couplers providing diffusible colored dyes can be used together with
the above mentioned couplers for improving graininess and specific
examples of these couplers are magenta couplers described in U.S. Pat. No.
4,366,237 and GB Pat. No. 2,125,570 and yellow, magenta and cyan couplers
described in EP Pat. No. 96,873, and in DE Pat. Appl. No. 3,324,533.
Also, among the 2-equivalent couplers are those couplers which carry in the
coupling position a group which is released in the color development
reaction to give a certain photographic activity, e.g. as development
inhibitor or accelerator or bleaching accelerator, either directly or
after removal of one or further groups from the group originally released.
Examples of such 2-equivalent couplers include the known DIR couplers as
well as DAR, FAR and BAR couplers. Typical examples of said couplers are
described in DE Pat. Appl. Nos. 2,703,145, 2,855,697, 3,105,026,
3,319,428, 1,800,420, 2,015,867, 2,414,006, 2,842,063, 3,427,235,
3,209,110, and 1,547,640, in GB Pat. Nos. 953,454 and 1,591,641, and in EP
Pat. Appl. Nos. 89,843, 117,511, 118,087, 193,389, and 301,477.
Examples of non-color forming DIR coupling compounds which can be used in
silver halide color elements include those described in U.S. Pat. Nos.
3,938,996; 3,632,345; 3,639,417; 3,297,445 and 3,928,041; in German patent
applications S.N. 2,405,442; 2,523,705; 2,460,202; 2,529,350 and
2,448,063; in Japanese patent applications S.N. 143,538/75 and 147,716/75
and in British patents 1,423,588 and 1,542,705.
In order to introduce the couplers into the silver halide emulsion layer,
some conventional methods known to the skilled in the art can be employed.
According to U.S. Pat. Nos. 2,322,027, 2,801,170, 2,801,171 and 2,991,177,
the couplers can be incorporated into the silver halide emulsion layer by
the dispersion technique, which consists of dissolving the coupler in a
water-immiscible high-boiling organic solvent and then dispersing such a
solution in a hydrophilic colloidal binder under the form of very small
droplets. The preferred colloidal binder is gelatin, even if some other
kinds of binders can be used.
Another type of introduction of the couplers into the silver halide
emulsion layer consists of the so-called "loaded-latex technique". A
detailed description of such technique can be found in BE patents 853,512
and 869,816, in U.S. Pat. Nos. 4,214,047 and 4,199,363 and in EP patent
14,921. It consists of mixing a solution of the couplers in a
water-miscible organic solvent with a polymeric latex consisting of water
as a continuous phase and of polymeric particles having a mean diameter
ranging from 0.02 to 0.2 micrometers as a dispersed phase.
Another useful method is further the Fisher process. According to such a
process, couplers having a water-soluble group, such as a carboxyl group,
a hydroxy group, a sulfonic group or a sulfonamido group, can be added to
the photographic layer for example by dissolving them in an alkaline water
solution.
The photographic elements, including a silver halide emulsion according to
this invention, may be processed to form a visible image upon association
of the silver halides with an alkaline aqueous medium in the presence of a
developing agent contained in the medium or in the material, as known in
the art. The aromatic primary amine color developing agent used in the
photographic color developing composition can be any of known compounds of
the class of p-phenylendiamine derivatives, widely employed in various
color photographic process. Particularly useful color developing agents
are the p-phenylendiamine derivatives, especially the
N,N-dialkyl-p-phenylene diamine derivatives wherein the alkyl groups or
the aromatic nucleus can be substituted or not substituted.
Examples of p-phenilene diamine developers include the salts of:
N,N-diethyl-p-phenylendiamine, 2-amino-5-diethylamino-toluene,
4-amino-N-ethyl-N-(.alpha.-methanesulphonamidoethyl)-m-toluidine,
4-amino-3-methyl-N-ethyl-N-(.alpha.-hydroxy-ethyl)-aniline,
4-amino-3-(.alpha.-methylsulfonamidoethyl)-N,N-diethylaniline, 4-amino-N,
N-diethyl-3-(N'-methyl-.alpha.-methylsulfonamido)-aniline,
N-ethyl-N-methoxy-ethyl-3-methyl-p-phenylenediamine and the like, as
described, for instance, in U.S. Pat. Nos. 2,552,241; 2,556,271; 3,656,950
and 3,658,525.
Examples of commonly used developing agents of the p-phenylene diamine salt
type are: 2-amino-5-diethylaminotoluene hydrochloride (generally known as
CD2 and used in the developing solutions for color positive photographic
material), 4-amino-N-ethyl-N-(.alpha.-methanesulfonamidoethyl)-m-toluidine
sesquisulfate monohydrate (generally known as CD3 and used in the
developing solution for photographic papers and color reversal materials)
and 4-amino-3-methyl-N-ethyl-N-(.beta.-hydroxy-ethyl)-aniline sulfate
(generally known as CD4 and used in the developing solutions for color
negative photographic materials).
Said color developing agents are generally used in a quantity from about
0.001 to about 0.1 moles per liter, preferably from about 0.0045 to about
0.04 moles per liter of photographic color developing compositions.
In the case of color photographic materials, the processing comprises at
least a color developing bath and, optionally, a prehardening bath, a
neutralizing bath, a first (black and white) developing bath, etc. These
baths are well known in the art and are described for instance in Research
Disclosure 17643, 1978.
After color development, the image-wise developed metallic silver and the
remaining silver salts generally must be removed from the photographic
element. This is performed in separate bleaching and fixing baths or in a
single bath, called blix, which bleaches and fixes the image in a single
step. The bleaching bath is a water solution having a pH equal to 5.60 and
containing an oxidizing agent, normally a complex salt on an alkali metal
or of ammonium and of trivalent iron with an organic acid, e. g.
EDTA.Fe.NH4, wherein EDTA is the ethylenediaminotetracetic acid. While
processing, this bath is continuously aired to oxidize the divalent iron
which forms while bleaching the silver image and regenerated, as known in
the art, to maintain the bleach effectiveness. The bad working of these
operations may cause the drawback of the loss of cyan density of the dyes.
Further to the above mentioned oxidizing agents, the blix bath contains
known fixing agents, such as for example ammonium or alkali metal
thiosulfates. Both bleaching and fixing baths can contain other additives,
e. g. polyalkyleneoxide derivatives, as described in GB patent 933,008 in
order to increase the effectiveness of the bath, or thioethers known as
bleach accelerators.
The present invention will be illustrated with reference to the following
examples, but it should be understood that these examples do not limit the
present invention.
EXAMPLE 1
Preparation of Silver Bromoiodide Emulsion 1 (invention)
A core-shell silver bromoiodide emulsion having a grain size of 1.5 .mu.m
was prepared according to the following procedure.
An aqueous solution prepared by dissolving 63.4 g of deionized gelatin,
18.9 g of potassium bromide, and 1.57 g of sodium thiocyanate in 2722 g of
distilled water was stirred by a dispersator at 3500 rpm and T=57.degree.
C.
A double jet addition of 37.4 ml of a silver nitrate solution (2.5M) and
94.6 ml of a potassium bromide solution (3.2M) was performed at constant
flow rate in two minutes. The emulsion was kept under stirring for 30
seconds.
After that, 680 ml of a silver nitrate solution (2.5M) were added with a
linear accelerated ramp (from 20 ml/min to 48 ml/min) and at the same time
a potassium bromide solution (3.2M) was added to change the pAg value
(measured with a Ag.sub.2 S/Calomel Electrode) from -83 mV to -63 mV. The
double-jet addition was completed in twenty minutes.
During the next five minutes, a silver nitrate solution (2.5M) was added at
constant flow rate (48 ml/min) and a potassium iodide solution (0.5M) was
added at constant flow rate of 11.1 ml/min by maintaining the pAg value at
-63 mV with a potassium bromide solution (3.2M).
During the next fourteen minutes, a silver nitrate solution (2.5M) was
added with a linear reversed ramp (from 48 ml/min to 10 ml/min). At the
same time a KBr solution (3.2M) was added in order to change the pAg from
-63 to +50 mV.
After one minute pause, 103.0 ml of an ammonia solution (12N) were added,
followed by the addition of 214.2 ml of a potassium iodide solution (0.5M)
in three minutes.
During the next twentyfive minutes, 452.5 ml of a silver nitrate solution
(2.5M) and 380 ml of a potassium iodide solution (0.5M) were added at
constant flow rate, by maintaining the pAg value at -10 mV with a
potassium bromide solution (3.2M). The pH was then reduced at 6.0
neutralizing the ammonia present in the system with a sulfuric acid
solution (25%).
Finally, 543 ml of a silver nitrate solution (2.5M) were added with
constant flow rate in 30 minutes by mantaining the pAg value at -10 mV
with a potassium bromide solution (3.2M).
EXAMPLE 2
Preparation of Silver Bromoiodide Emulsion 2 (comparison)
A core-shell silver bromoiodide emulsion having a grain size of 1.5 .mu.m
was prepared according to the following procedure.
An aqueous solution prepared by dissolving 63.4 g of deionized gelatin,
18.9 g of potassium bromide, and 1.57 g of sodium thiocyanate in 2722 g of
distilled water was stirred by a dispersator at 3500 rpm and T=57.degree.
C.
A double jet addition of 37.4 ml of a silver nitrate solution (2.5M) and
94.6 ml of a potassium bromide solution (3.2M) was performed at constant
flow rate in two minutes. The emulsion was kept under stirring for 30
seconds.
After that, 680 ml of a silver nitrate solution (2.5M) were added with a
linear accelerated ramp (from 20 ml/min to 48 ml/min) and at the same time
a potassium bromide solution (3.2M) was added to change the pAg value
(measure with a Ag.sub.2 S/Calomel Electrode) from -83 mV to -63 mV. The
double-jet addition was completed in twenty minutes.
During the next fourteen minutes, a silver nitrate solution (2.5M) was
added with a linear reversed ramp (from 48 ml/min to 10 mlmin). At the
same time a KBr solution (3.2M) was added in order to change the pAg from
-63 to +50 mV.
During the next twentyfive minutes, 452.5 ml of a silver nitrate solution
(2.5M) and 380 ml of a potassium iodide solution (0.5M) were added at
constant flow rate, by maintaining the pAg value at -10 mV with a
potassium bromide solution (3.2M).
Then, 539.4 ml of a silver nitrate solution (2.5M) and 269.7 ml of a silver
iodide solution (0.5M) were added with constant flow rate in 30 minutes by
mantaining the pAg value at -10 mV with a potassium bromide solution
(3.2M).
Finally, 244.4 ml of a silver nitrate solution (2.5M) were added with
constant flow rate in 13.5 minutes by mantaining the pAg value at -10 mV
with a potassium bromide solution (3.2M).
EXAMPLE 3
Preparation of Silver Bromoiodide Emulsion 3 (comparison)
A core-shell silver bromoiodide emulsion having a grain size of 1.5 .mu.m
was prepared according to the following procedure.
An aqueous solution prepared by dissolving 63.4 g of deionized gelatin,
18.9 g of potassium bromide, and 1.57 g of sodium thiocyanate in 2722 g of
distilled water was stirred by a dispersator at 3500 rpm and T=57.degree.
C.
A double jet addition of 37.4 ml of a silver nitrate solution (2.5M) and
94.6 ml of a potassium bromide solution (3.2M) was performed at constant
flow rate in two minutes. The emulsion was kept under stirring for 30
seconds.
After that, 680 ml of a silver nitrate solution (2.5M) were added with a
linear accelerated ramp (from 20 ml/min to 48 ml/min) and at the same time
a potassium bromide solution (3.2M) was added to change the pAg value
(measured with a Ag.sub.2 S/Calomel Electrode) from -83 mV to -63 mV. The
double-jet addition was completed in twenty minutes.
During the next five minutes, a silver nitrate solution (2.5M) was added at
constant flow rate (48 ml/min) by maintaining the pAg value at -63 mV with
a potassium bromide solution (3.2M).
During the next fourteen minutes, a silver nitrate solution (2.5M) was
added with a linear reversed ramp (from 48 ml/min to 10 ml/min). At the
same time a KBr solution (3.2M) was added in order to change the pAg from
-63 to +50 mV.
After one minute pause, 238.8 ml of a potassium iodide solution (0.5M) were
added in three minutes at constant flow rate.
518.9 ml of a silver nitrate solution (2.5M) and 435.5 ml of a potassium
iodide solution (0.5M) were added in 28 minutes and 40 seconds at constant
flow rate, by maintaining the pAg value at -10 mV with a potassium bromide
solution (3.2M).
Finally, 476.6 ml of a silver nitrate solution (2.5M) were added with
constant flow rate in 26 minutes and 20 seconds by mantaining the pAg
value at -10 mV with a potassium bromide solution (3.2M).
EXAMPLE 4
Preparation of Silver Bromoiodide Emulsion 4 (invention)
A core-shell silver bromoiodide emulsion having a grain size of 1.1 .mu.m
was prepared according to the following procedure. An aqueous solution
prepared by dissolving 63.4 g of deionized gelatin, 18.9 g of potassium
bromide, and 1.57 g of sodium thiocyanate in 2722 g of distilled water was
stirred by a dispersator at 3500 rpm and T=57.degree. C.
A double jet addition of 37.4 ml of a silver nitrate solution (2.5M) and
94.6 ml of a potassium bromide solution (3.2M) was performed at constant
flow rate in two minutes. The emulsion was kept under stirring for 30
seconds.
After that, 680 ml of a silver nitrate solution (2.5M) were added with a
linear accelerated ramp (from 20 ml/min to 48 ml/min) and at the same time
a potassium bromide solution (3.2M) was added to change the pAg value
(measure with a Ag.sub.2 S/Calomel Electrode) from -83 mV to -63 mV. The
double-jet addition was completed in twenty minutes.
During the next ten minutes, a silver nitrate solution (2.5M) was added
with a linear reversed ramp (from 40 ml/min to 8 ml/min). At the same time
a KBr solution (3.2M) was added in order to change the pAg from -63 to +50
mV.
After one minute pause 103 ml of ammonia solution (12M) were added.
Then, 518.9 ml of a silver nitrate solution (2.5M) and 435.5 ml of a
potassium iodide solution (0.5M) were added in 28 minutes at constant flow
rate, by maintaining the pAg value at -10 mV with a potassium bromide
solution (3.2M).
After one minute pause, 214.7 ml of a potassium iodide solution (0.5M) were
added in three minutes at constant flow rate.
Then, the pH was reduced at 6.0, neutralizing the ammonia present in the
system with a sulfuric acid solution (25%).
Finally, 884.0 ml of a silver nitrate solution (2.5M) were added with
constant flow rate in 40 minutes by mantaining the pAg value at -10 mV
with a potassium bromide solution (3.2M)
The following table 1 summarizes the core-shell structure of emulsions 1 to
4.
TABLE 1
Emulsion 1* Emulsion 2 Emulsion 3** Emulsion 4***
% Ag AgI % % Ag AgI % % Ag AgI % % Ag AgI %
Core 30.4 0.0 47.6 0.0 56.0 0.0 40.6 0.0
I 10.2 4.6 19.2 16.8 22.0 16.8 20.2 16.8
Shell
II 15.4 0.0 22.8 10.0 20.2 0.0 37.4 0.0
Shell
III 19.2 16.8 10.4 0.0 -- -- -- --
Shell
IV 23.0 0.0 -- -- -- -- -- --
Shell
*Emulsion 1 has a pure iodide phase representing 1.8% of the total Ag
between shells II and III
**Emulsion 3 has a pure iodide phase representing 1.8% of the total Ag
between core and shell I
***Emulsion 4 has a pure iodide phase representing 1.8% of the total Ag
between shell I and shell II
All the emulsions were optimally chemically digested with gold and sulfur
using p-toluenethiosulfonic acid p-toluenesulfinic acid and gold
tetrachloroaurate complexed with potassium thiocyanate.
A magenta monochrome film was obtained from each emulsion 1 to 4 by using
green sensitizing dyes S-4 and S-5, magenta coupler M-1 and conventional
coating formulation. The silver coverage of the magenta layer was 1.50 g
Ag/m.sup.2. Samples of each film were exposed to a white light source
having a color temperature of 5,500 Kelvin. All the exposed samples were
developed in a standard type C41 process as described in British Journal
of Photography, Jul. 12, 1974, pp. 597-598. The sensitometric results are
showed in the following Table 2. The graininess was visually evaluated on
the developed samples by means of scholastic scores ranging from 5 to 10.
TABLE 2
Dmin Dmax Speed 0.2 Speed 1.0 Graininess
Emulsion 1 0.17 3.19 2.78 2.30 9
(Invention)
Emulsion 2 0.17 3.03 2.71 2.20 7
(Comparison)
Emulsion 3 0.17 3.35 2.38 1.76 10
(Comparison)
Emulsion 4 0.18 2.80 2.70 2.15 9.5
(Invention)
The data of Table 2 clearly show the superior overall characteristics of
the silver halide emulsions of the present invention. By comparing
emulsion 1 of the invention with comparison emulsions 2 and 3 having the
same grain size, the results show the best compromise in terms of
sensitometric characteristics (Dmin, Dmax, and speed) and graininess.
Comparison emulsion 2 in spite of having similar sensitometric results
shows an unacceptable grainininess. Comparison emulsion 3 in spite of
having an excellent graininess has unacceptable sensitometric
characteristics. Emulsion 4 of the invention (which has a lower grain
size) still shows sensitometric results comparable to those of comparison
emulsion 2 with an excellent grain size.
Formulas of compounds used in the present invention will be presented
below.
Green Sensitizer S-4
##STR1##
Green Sensitizer S-5
##STR2##
Magenta Coupler M-1
##STR3##
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